Side Effects of Insulin in Cats

Insulin is a lifesaving medication for cats diagnosed with diabetes, but it does have a few drawbacks. If a vet has determined a cat is insulin-dependent, it will likely require insulin injections for the rest of its life. Insulin can cause potentially fatal drops in blood sugar. Insulin use also takes a hit on cat owners' pocketbooks---in 2010, it retails at around $115 per 100-unit vial and necessitates frequent visits to the vet's office.

  1. Hypoglycemia

    • Hypoglycemia, or low blood sugar, is one of the most common side effects of insulin. It's also one of the most dangerous. It occurs when too much insulin has been delivered or a cat is more active than usual. Fluctuations in a cat's eating habits can also lead to hypoglycemia. According to Cornell University's College of Veterinary Medicine, symptoms include weakness, listlessness, lack of coordination, convulsions and coma.

      Hypoglycemia is potentially fatal and must be treated immediately. If your cat exhibits symptoms of hypoglycemia, offer it some of its regular food. If it can't or doesn't eat, rub corn syrup onto its gums. Do not force-feed a cat during a hypoglycemic event. Insulin-induced hypoglycemia can be frightening for cat and owner alike. Work with your vet to establish a blood sugar control regime that does not lead to frequent bouts of hypoglycemia. Long-acting insulin such as Lantus and Levemir can cause hypoglycemia, as can short-acting insulin. Use of short-acting insulin in the treatment of diabetes in cats is not widespread.

    Ineffective Absorption

    • Injecting insulin into the same site day after day will lead to the formation of a granuloma, or a lump of tissue. Because blood supply to granulomas is poor, insulin will not be optimally absorbed. Rotate injection sites to avoid this problem.

    Somogyi Effect

    • Swings between high and low blood sugars tire a cat.

      The Somogyi effect is a roller-coaster ride initiated by insulin-instigated hypoglycemia. It activates a cat's natural defense system. Once there is more insulin in the bloodstream than a cat's body requires, blood sugar plummets. This creates production of hormones including epinephrine, which leads to a breakdown of glycogen. Glycogen is a store of glucose in the liver. Once glycogen is released, blood sugar rockets upward and creates a rebound hyperglycemia, or high blood sugar. Consult with your vet if this occurs. Symptoms of hyperglycemia are the same as those likely presented when your cat was diagnosed with diabetes: increased thirst and urination, depression, weight loss and wounds that won't heal.

    Antibody Production

    • An uncommon but possible side effect of insulin use is the creation of antibodies. The cat's body may treat injectable insulin as a hostile intruder and form antibodies to attack the medication. Consult your vet if your cat is not responding to insulin.